The graphic arts industry commonly employs systems for removing sheets or signatures separately from a stack of signatures, such as in the process of gathering or collating the removed signatures. In that well-known function, the bottom one of a stack of sheets or signatures is taken from the stack while the rest of the stack remains in position, with the bottom sheet or signature being removed from the stack, one-by-one. In that process, it is common practice, and commonly preferred, that the stack be in at least a reclining position where the weight of the stack bears downwardly on the bottom signature. Therefore, the removal of the bottom signature or sheet is impaired, because of the weight of the stack on it.
To facilitate the removal of the sheet, the prior art has resorted to devices for somewhat supporting the stack while the sheet is removed, and one such device is a commonly employed rotating disk which slides between the bottom sheet and the remainder of the stack while the bottom sheet is moved below the rotating disk. Other types of supports for the entire stack are sometimes utilized, such as that shown in U.S. Pat. No. 3,527,367 where a stop and a clamp are disclosed for controlling the stack.
In the instance where the prior art utilizes the rotating disk mentioned, there are inherent problems, such as the concern about the disk sliding over the bottom of the stack and thereby distorting and marring the bottom signature or sheet. The rotating disk can move the bottom sheet out of registration or alignment, and thus the handling of that sheet or signature is impaired. Further, each time that the rotating disk sweeps underneath the pile or stack, the stack bounces and this creates control problems and undesirable vibrations.
The present invention improves upon the prior art in that it provides both a method and apparatus for controlling the stack of sheets or signatures in a tray or hopper, and the control is such that the entire weight of the stack does not bear downwardly toward the bottom sheet or signature which is to be removed. In that respect, the bottom sheet is not damaged in removal and is not moved out of line, since the bottom sheet is in a freer state for removal, since the entire weight of the stack does not bear downwardly on the bottom sheet. In this regard, there is an escapement device which presents only a limited number of sheets to the removal process or apparatus, and thus the improved control is achieved in this invention, compared to the prior art.
Still further, the present invention improves upon the prior art in that it provides both a method and apparatus which can be readily incorporated in the prior art existing apparatus of a hopper with a rotating disk and a suction member or the like for removing the bottom sheet. It will of course be understood that the graphic arts industry already has a considerable number of stack hoppers and removal devices already in existence. The present invention is completely suitable for incorporation into the existing devices, with a minimum of material and with no appreciable revision or reconstruction of any of the existing apparatus.
The present concept or invention is for allowing a discrete quantity of sheets or signatures to be fed downwardly in a hopper in a controlled manner while relieving the weight of the remainder of the stack or pile from that sheet separating area, all so that the bottom sheet or signature can be removed with only a minimum of resistance thereon.